This invention relates to plasma etching and, more particularly, to apparatus for and process of plasma etching.
With recent trend for increasing integration density, more and more LSIs (large scale integrated circuit) are being replaced with VLSIs (very large scale integrated circuit), and this is requiring the replacement of wet etching process with dry etching process in the manufacture of such semiconductor devices. Particularly, reactive ion etching has been extensively used as the dry etching process. In the reactive ion etching process, reactive gas is introduced into a space between a pair of flat plate electrodes disposed parallel to and facing each other, and is dissociated through discharge caused by application of high frequency power to one of the electrodes, thus producing plasma. Positive ions in the plasma thus produced are accelerated by a negative self-bias generated on the workpiece and caused to bombard the workpiece, which is placed on the electrode to which the high frequency power is applied. In this way, the etching of the workpiece is effected. Highly precise patterns can be formed by the reactive ion etching using, for instance, such gases as CHF.sub.3 and a gas mixture of CF.sub.4 and H.sub.2 in such case as when forming contact holes in a SiO.sub.2 film formed on a semiconductor substrate. High precision etching of polycrystalline silicon used as the electrode material can be obtained by using such gases as CBrF.sub.3 and a gas mixture of CBrF.sub.3 and Cl.sub.2. Further, such gases as CCl.sub.4 and a gas mixture of CCl.sub.4 and Cl.sub.2 can be used for the high precision etching of Al and Al alloys serving as the interconnection electrode material.
Among the aforementioned combinations of reactive gases and workpiece materials, particularly chlorine-containing gases used for etching Al or Al alloys, unlike the other combinations, present many problems because of the very strong corrosive action upon the Al and Al alloys and the difficulty of removing the oxide film (Al.sub.2 O.sub.3) on the Al or Al alloy surface. For example, the reproducibility of etching is inferior due to a delay time involved at the commencement of etching. Also, undesired residue results from the etching. Further, after the workpiece material is taken out to the atmosphere, corrosion of Al or Al alloy is observed.
Among these problems, the reproducibility has been found to be extremely improved, as a result of research and investigations by the inventors, by using a mixture of CCl.sub.4 and Cl.sub.2 as the reactive gas and minimizing the effects of H.sub.2 O on the etching. However, the problem of the corrosion of the workpiece material has not yet been solved. This corrosion is thought to be caused by HCl generated as a result of hydrolysis of Cl.sub.2 occurring when the workpiece material is taken out from the etching chamber to the atmosphere after the etching. There is a well-known method of preventing such corrosion of the workpiece material, in which the process material is not taken out to the atmosphere immediately after the etching but is exposed to O.sub.2 plasma in the same etching chamber, thus covering the processed surface with oxide. With this method, however, the process with O.sub.2 plasma in the etching chamber is greatly influenced by Cl.sub.2 remaining in the etching chamber, and therefore the prevention of the corrosion of the workpiece material is insufficient. In addition, O.sub.2 plasma is liable to cause damage to an organic film coated on the electrodes and etching chamber inner walls.
The corrosion of the workpiece material often gives rise to such problems as extreme difficulty of the subsequent removal of resist, defective isolation in the patterning of interconnection electrodes and reduction of the reliability of elements due to Cl.sub.2 remaining on the workpiece material surfaces.